Should we all be using heat pumps?

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This morning CAT Renewable Energy lecturer and researcher Tobi Kellner has been on the BBC Breakfast Programme, the Today Programme and BBC News talking about heat pumps. The National Trust is installing water source heat pumps in Plas Newydd and Tobi commented on whether these could be something that was rolled out across the UK, and what the environmental impact of that would be. Tobi expands on what the potential for heat pumps is for householders, and the UK generally.

Heat pumps advice for householders

In my role as renewable energy consultant – and when I worked for CAT’s free Information Service – I often talk to householders who are enthusiastic about renewable energy and want to install a heat pump. However, I generally advise against installing heat pumps in typical UK properties – buildings heated by a gas boiler that is connected to normal radiators. Results from field trials suggest that under these conditions heat pumps typically achieve seasonal performance factors of between 2.0 and 2.5 – that means they supply between 2.0 and 2.5 units of heat for every unit of electricity they consume. That sounds impressive – “up to 250% efficiency”, as some sales brochures would put it. But at the moment most of our electricity is still produced by very inefficient fossil fuel power stations. For example, a coal power station needs three units of heat from coal to produce a unit of electricity. If you now use that unit of electricity to power a heat pump that delivers two units of heat to a building then you’d actually be better off burning coal directly! Our calculations suggest that for existing homes which are on the mains gas grid heat pumps have no significant advantage in terms of money or carbon emissions – much better idea to invest money in improving insulation or maybe installing a solar roof.

An air-source heat pump at CAT

On the other hand, I also advise people who want to build new homes, and here heat pumps can often be a great choice: If you build to a very high standard of energy efficiency (as any new building should be!) and if you design a heating system that can run at fairly low temperatures (for example, underfloor heating with densely spaced pipes can run at 35°C whereas radiators may need 70°C) then heat pumps can be an excellent choice.

Heat pumps in the Graduate School of the Environment

As a lecturer in CAT’s Graduate School of the Environment, I currently supervise a student carrying out research into heat pumps for his M.Sc. thesis. Having wired up his own heat pump and house with sensors and data loggers over the last winter, the student built a computer model that allows him to answer questions such as Would the heat pump be able to supply enough heat during a cold winter if it only operates during times of low electricity demand?
Answering question of this type is crucial for our transformation to a renewably powered future, and it’s great to see that our students are taking a lead!

Tobi and the ZCB team outside parliament

Heat pumps in Zero Carbon Britain

In our Zero Carbon Britain scenario, heat pumps play a central role. When we looked at how we could supply 100% of our energy from UK-based renewables, we noticed two things: First, wind turbines will play a central role in our energy supply as the UK has a fantastic wind resource. And second, even though we assume that in ZCB our buildings will be much better insulated than today, we will still need a lot of heat energy to keep us warm. And in many ways, wind turbines and heat pumps are “a match made in heaven”. On average, we have more wind power in winter when we need more heat (though there are of course periods when it is cold but calm), so there’s a nice match between supply and demand. And heat pumps can even help us deal with variability from renewable electricity sources. You wouldn’t want your lights to go dim whenever the wind blows a bit less. But heat is very easy to store – in the form of hot water, or even in the ‘thermal mass’ of the bricks & mortar of our homes. So you can easily imagine a future where your heat pump works harder at times when there is plenty of wind and little demand (e.g. during a windy night) and stop working during times of peak demand or low renewable energy supply. Our research suggests this could play a significant role in powering future energy supplies, without any impact on comfort. For more information on the role of heat pumps in Zero Carbon Britain, download the report here.